1. Field of the Invention
The present invention relates to a temperature sensor having as a temperature-sensitive element, a thermistor formed from a semiconductor such as a metal oxide, a metal resistor, or the like accommodated in a metal cap or a metal tube.
2. Description of the Related Art
A conventionally known temperature sensor includes a sheath member which insulates and holds metal core wires connected at their tip ends to a temperature-sensitive element and connected at their rear ends to corresponding lead wires for connection to an external circuit; a metal cap circumferentially joined to the sheath member while accommodating the temperature-sensitive element therein; and a mounting member supporting the sheath member with the metal cap and a tip end portion of the sheath member exposed to the exterior thereof, and having a mounting seat adapted to abut a sensor-mounting seat (Patent Document 1 (FIG. 4) and Patent Document 2 (FIG. 1)).
Another known temperature sensor includes a longitudinally extending metal tube having a closed tip end; a temperature-sensitive element accommodated within the metal tube and having an electric characteristic that varies with temperature; and a mounting member supporting the metal tube with a tip end portion of the metal tube exposed to the exterior thereof, and having a mounting seat adapted to abut a sensor-mounting seat (Patent Document 1 (FIGS. 1 and 2)).
These temperature sensors are used to detect the temperature of a measurement object (exhaust gas or the like) in an environment subject to strong vibrations, such as the interior of an automotive catalytic converter, an automotive exhaust pipe, or the like.                [Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2002-350239        [Patent Document 2] Japanese Patent Application Laid-Open (kokai) No. 2000-162051        
3. Problems to be Solved by the Invention
However, in the case where the resonance frequencies (primary resonance frequencies) of the above-mentioned conventional temperature sensors overlap a frequency band of vibrations generated in an environment where the temperature sensors are installed, there is the risk of breaking a wire or an electric path within the temperature sensor, breakage of the sheath member or the metal tube, or a like problem.
Particularly, when a tip end projection length as measured longitudinally between the mounting seat of the mounting member and the tip end of the metal cap is long, the resonance frequency of a sensor is highly likely to overlap a frequency band of vibrations generated in an environment where the sensor is installed.
A conceivable remedy, for example, is to shorten the longitudinal distance between the mounting seat of the mounting member of the temperature sensor and the tip end of the metal cap (or the metal tube) (tip end projection length).
However, in certain environments where a sensor is installed, a long distance lies between a temperature-detecting position and a sensor-mounting seat that the mounting seat of the sensor abuts. In application to such an environment, shortening of the tip end projection length is limited, so that there is a need to prevent the wires from breaking or to prevent other breakage due to resonance.